1. Field of the Invention
This invention relates generally to retainer cups for captive screw assemblies that are used to secure together parts or subassemblies. More particularly, the invention is directed to captive screw assemblies for securing a subassembly having at least a ductile portion to another part, subassembly, or member, and that resist disengagement from the subassembly when placed under stress.
2. Description of the Related Art
In the electronics and other industries, it is often desirable to secure with fasteners various subassemblies to parts, frames, members, or other subassemblies so as to form an integrated structure that may then be placed under, or be subjected to, stress. The stress tends to force the fasteners to separate from the subassemblies, thereby weakening the entire structure. In such situations, the fastener may become entirely detached from the subassembly and structure and fall out, thereby rendering the structure unstable, misaligned, or entirely disassembled. This will inevitably cause a decrease in performance of the entire system in which the structure is integrated, or may cause a complete failure of the system. Furthermore, in commercial or consumer settings, children may find the loose fasteners and inappropriately play with them by, for example, placing the fasteners in their mouths, presenting a potential choking hazard.
This problem has been at least partially addressed in the metal fabrication industry with various kinds of captive fasteners for holding metal objects to one another or to various other devices or frame members. In the building arts, various and sundry capturing mechanisms, such as anchors and rawls, have long been employed to secure fasteners in wallboard and wood panels, for example, so that structures constructed of these members will maintain composite integrity. However, in all other areas that employ plastic subassemblies and/or structures formed at least partially of softer and more ductile materials, a suitable captive fastener has not been developed that will securely seat in the subassemblies and remain permanently affixed thereto when stresses are applied to the resulting structures. Accordingly, at the present time structures of this nature tend to loosen and fall apart under stress and/or over time, causing degradation of the systems employing these subassemblies. For example, in the electronics industry, circuit packs, which generally comprise ductile plastics, often lose screws and fasteners intended to hold multiple circuit packs together or to their modular frames. This degrades circuit performance and often results in circuit and system failures.
There is thus a long-felt, unfulfilled need in the art for captive fastener assemblies for use in securing devices, parts, or subassemblies formed at least in part of soft, ductile materials to one another and/or to other devices or elements so as to form useful integrated or composite structures and assemblies.